When you are preparing to interview for a Java programming job, it’s important to consider the questions you’ll be asked. These interview questions can vary based on many factors, including company type, role level, and how long the company you interview with has been in business. How can you prepare to answer these questions with so much to consider?

Prep for a Java interview by thinking about examples that demonstrate your Java programming skills and capabilities. You can also think of scenarios and past experiences that speak to your understanding of Java programming concepts. We recommend you brainstorm some ideas and write them down. If you keep a list of your examples, you can quickly refer to them when you prepare to interview.

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Another useful interview strategy is to review potential Java interview questions in advance. Let’s check out examples of some of the top Java interview questions. Also, each question includes some information that can help refresh your memory. 

The topics we will cover include: 

The more you know about these topics, the better prepared you will be to answer your Java interview questions with flying colors!

General Java interview questions

  1. What is Java?

Java is a platform-independent high-level programming language. It is platform-independent because its byte codes can run on any system regardless of its operating system.

  1. What are the features of Java?
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  1. What are the OOP concepts?
  1. What is data encapsulation, and why is it useful?

Encapsulation is a concept in Object-Oriented Programming for combining properties and methods in a single unit. Encapsulation helps developers follow a modular approach for software development because each object has its own set of methods and variables and serves its functions independent of other objects. In addition to that, encapsulation serves data hiding purposes.

  1. What is polymorphism?

Polymorphism is one interface with many implementations. This characteristic allows you to assign a different meaning or usage to something in different contexts. For example, you can use polymorphisms to enable more than one form for entities, such as variables, functions, or objects.

  1. What are the types of polymorphism, and how do they differ?

There are two types of polymorphism:

  1. What does an interface in Java refer to?
  1. What are constructors in Java?

In Java, a constructor refers to a block of code used to initialize an object. In addition:

  1. Name and explain the types of constructors in Java.

The two types of constructors in Java are the Default Constructor and the Parameterized Constructor.

  1.  What is JDK?
  1.  What is JVM?
  1.  What is JRE?
  1.  In Java, what are the differences between heap and stack memory?

Memory

Access

Memory Management

Lifetime

Usage

  1.  What is a JIT compiler?

A JIT compiler runs after the program is executed and compiles the code into a faster form, hosting the CPU’s native instructing set. 

  1.  How does a JIT compiler differ from a standard compiler?

JIT can access dynamic runtime information, and a standard compiler does not. Therefore, JIT can better optimize frequently used inlining functions.

  1.  What is an inner class?

An inner class is a class that is nested within another class. An Inner class has access rights for the class that is nesting it, and it can access all variables and methods defined in the outer class.

  1.  What is a subclass?

A subclass is a class that inherits from another class called the superclass. Subclass can access all public and protected methods and fields of its superclass.

  1.  What is a package in Java?

In Java, packages are the collection of related classes and interfaces which bundle together. 

  1.  How can developers use packages in Java?

Packages in Java allow developers to modularize the code and optimize its reuse easily. In addition, developers can use other classes to import and reuse the code within the packages. 

  1.  What are the advantages of packages in Java?

Java class, variable, objects, and argument questions

  1.  What is a class in Java?

All Java codes are defined in a class. It has variables and methods.

  1.  What is a variable within Java?

Variables are attributes that define the state of a class.

  1.  How do you use a method in Java?

Methods are the place where the exact business logic has to be done. Methods contain a set of statements or instructions that satisfy specified requirements. 

  1.  What is a Java object?

An object is an instance of a class. The object has a state and behavior.

  1.  What is a singleton class, and how can it be used?

A singleton class in Java can have only one instance. Therefore, all its methods and variables belong to this instance. The singleton class concept is useful when the developer needs to limit the number of objects for a class.

  1.  What is a constructor in Java?

The sole purpose of using Constructors in Java is to create an instance of a class. Creating an object of a class will invoke them. Some key features of Java constructors include:

  1.  What does the term constructor overloading mean?

Constructor overloading indicates passing different numbers and types of variables as arguments, all of which are private variables of the class.

  1.  How are non-primitive variables used in Java?

Non-primitive variables always refer to objects in Java.

  1.  In Java, what is a static variable?

A static variable is associated with a class and not objects of that class.

  1.  What are Java data types, and how are they grouped?

In Java, a variable must be a specified data type such as an integer, floating-point number, character Boolean, or string. The two groups of data types are:

  1.  How do you define primitive data types and describe each by size and description?
  1.  What do the terms autoboxing and unboxing mean in Java?
  1.  What are wrapper classes in Java?
  1.  In Java, what are the differences between methods and constructors?
MethodsConstructors
Used to represent the behavior of an object.Used to initialize the state of an object.
Must have a return type.Does not have a return type.
Needs to be invoked explicitly.Invoked implicitly.
The compiler does not provide a default method.The compiler provides a default constructor if the class has none.
Method name may or may not be the same as class name.Constructor name must always be the same as the class name.
  1.  Can you override a private method or static method in Java?

You cannot override a private or static method in Java. You cannot override a private method in subclass because it’s not accessible there.

  1.  What is method hiding?

Method hiding is an alternative to overriding a private or static method, which occurs when you hide the superclass method. You create a similar method with the same return type and same method arguments in child class. For example, you can create another private method with the same name in the child class.

  1.  What is the difference between equals() and == in Java?
  1.  Can you write multiple catch blocks under a single try block?

Yes, you can have multiple catch blocks under a single try block. Your approach should be from specific to general, as shown in the following example:

public class Example {

public static void main(String args[]) {

try {

int a[]= new int[10];

a[10]= 10/0;

}

catch(ArithmeticException e)

{

System.out.println(“Arithmetic exception in first catch block”);

}

catch(ArrayIndexOutOfBoundsException e)

{

System.out.println(“Array index out of bounds in second catch block”);

}

catch(Exception e)

{

System.out.println(“Any exception in third catch block”);

}

}

  1.  What is a local variable?

Local variables are defined in the method and scope of the variables that exist inside the method itself.

  1.  What is an instance variable?

An instance variable is defined inside the class and outside the method. The scope of the variables exists throughout the class.

  1.  How do you use final keywords and final variables in Java?
  1.  What is inheritance in Java?

Inheritance in Java is the concept where the properties of one class can be inherited by the other. It helps to reuse the code and establish a relationship between different classes.

  1.  In Java, what types of classes perform inheritance?
  1.  What types of inheritance does Java support?
  1.  What is Java exception handling?

In Java, exceptions are objects. When you throw an exception, you throw an object. However, you can’t throw just any object as an exception — only those objects whose classes descend from throwable. Throwable serves as the base class for an entire family of classes, declared in java.lang, that your program can instantiate and throw.

  1.  What are the differences between unchecked exception, checked exception, and errors?
  1.  What are loops in Java?

You would use a loop to execute a statement or a block of statements repeatedly. 

  1.  What are the types of loops in Java, and how are they used?
  1.  What is an infinite loop?

An infinite loop runs without any condition and runs infinitely. You can break an infinite loop by defining any breaking logic in the body of the statement blocks.

  1.  How do you declare an infinite loop?

for (;;)

{

    // Statements to execute

    // Add any loop breaking logic

}

  1.  What is the difference between the continue and break statement?

Break and continue are two important keywords used in loops. When using a break keyword in a loop, the loop breaks instantly. The current iteration breaks when using the continue keyword, and the loop continues with the next iteration.

Java string interview questions

  1.  What is the entry point in Java, and how is it written?
  1.  In Java, what are public static void main string args?

Public static void main string args, also known as public static void main(String[] args), means:

  1.  In Java, what’s the purpose of static methods and static variables?

Developers use a static keyword to make a method or variable shared for all objects when there is a requirement to share a method or a variable between multiple objects of a class. This is used instead of creating separate copies for each object.

  1.  How do you use, call, and access a static method in Java?
  1.  How do you use, call, and access a non-static method in Java?
  1.  In Java, what are this() and super(), and where are you required to use them?

In Java, super() and this() are special keywords used to call the constructor. When using this() and super(), they must be the first line of a block.

  1.  What does this() represent, and how is it used in Java?
  1.  What does super()represent, and how is it used in Java?
  1.  What is a Java switch statement, and how can it be used?
  1.  What is the default of the switch case? 

In a switch statement, the default case executes when no other switch condition matches. Because the default case is optional, you can only declare it after coding all other switch cases.

This comprehensive list of Java interview questions should have you better prepared for an interview, and not only that but a successful one. Make sure to write down your answers as you prepare, so you can better remember them. Ensure you practice — even in front of a mirror. Knowing how you sound and appear will only boost your confidence and make you better able to land that dream Java job you’ve been wanting. 

If you feel like you need to brush up on your skills, you can take some refresher Java courses. And check out these Java interview preparation courses offered on Udemy as well.

Page Last Updated: May 2022

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